Hex Nuts aka Hex Finish Nuts

The Standard Hex Nut

Finish nuts, also known as finished nuts, hex nuts, and finish hex, are used for many fastening applications. Hex finish nuts are often used with hex cap screws, socket screws and bolts when mechanically joining materials together.

If the size of the screw that you are using is smaller than 1/4-20 (ex 8-32 or 10-24) you should be using and searching for hex machine screws. Hex finish nuts start at size 1/4-20 and go all the way up to 1-1/4", they are available in fine thread and coarse thread.